1. Field of the Invention
The present invention relates to an image display medium, and more particularly to a repeatedly rewritable image display medium using coloring particles.
2. Description of the Related Art
Conventionally, as display technology using toner, an image display medium having conductive coloring toner and white particles sealed in a predetermined gap between a display side electrode substrate and a non-display side electrode substrate disposed opposite to the display side electrode substrate has been proposed (xe2x80x9cToner Displayxe2x80x9d, Japan Hardcopy ""99 Papers, pp. 249-252, Japan Hardcopy ""99 Fall Papers, pp. 10-13). In such an image display medium, an electric charge is applied to the conductive toner through a charge conveying layer disposed on the electrode inner surface of the non-display side electrode substrate. By action of an electric field generated between the two electrode substrates, the charged conductive coloring toner moves to the display side electrode substrate disposed opposite to the non-display side electrode substrate. As a result, the conductive coloring toner adheres to the inner side of the display side electrode substrate, so that an image is displayed by the contrast between the conductive coloring toner and white toner.
In conventional image display mediums, however, when conductive toner and particles are sealed between the electrode substrates of the image display medium in an environment having, for example, a temperature of 25xc2x0 C. and humidity of 50%, water vapor content in the gap between the two electrode substrates is 11.5 g/m3. When the image display medium is used in an environment having an external air temperature of 10xc2x0 C., dew condensation occurs on the surface of the conductive toner, on the surface of the particles and on the electrode substrate surfaces in the gap since saturated water vapor content at 10xc2x0 C. is 9.39 g/m3. Thus, the water vapor pressure in the gap between the display side electrode substrate and non-display side electrode substrate of the image display medium is determined by the environmental atmosphere at which the display side electrode substrate and non-display side electrode substrate are sealed. Accordingly, when the image display medium is used in an environment having a different external air temperature, dew condensation may occur on the surfaces of the electrode substrates, and on the surfaces of the conductive toner and particles within the gap. Further, the higher the water vapor content, the less the charge amount of the conductive toner becomes. When the charge amount of the conductive toner becomes less than a predetermined level, the conductive toner cannot be moved by the electric field formed between the substrates. As a result, favorable display characteristics cannot be obtained.
The present invention has been devised in light of the above problems. It is an object of the present invention to provide an image display medium that can maintain stable display characteristics without dew condensing on a display substrate surface or on particles in almost all environments in which the image display medium is presumed to be used, even if there are changes in the environment external to the image display medium.
According to a first aspect of the invention, an image display medium comprises: a pair of substrates, at least one of the substrates being light permeable; a gap disposed between the substrates; and plural kinds of particle groups differing in color and charging characteristic, the particle groups being sealed in the gap between the substrates and movable between the substrates by an electric field applied to the particles, wherein water vapor content in the gap is in a range in which dew does not condense in an environment in which the image display medium is used.
According to the invention of the first aspect, the image display medium is provided with a transparent display substrate, the display substrate including an electrode and being disposed at the image display surface side of the image display medium, and a back substrate, the back substrate including an electrode and being disposed opposite to the display substrate. A gap is formed between the display substrate and the back substrate. Plural kinds of particle groups differing in color and charge characteristics are sealed in the gap. The particle groups can move between the pair of substrates by an electric field created by applying voltage between the pair of electrodes. The gap includes a predetermined amount of water vapor within a predetermined temperature range to prevent dew condensation. Therefore, there is no dew condensation on the surfaces of the display substrate and the back substrate, or on the particle groups sealed in the gap in almost all environments in which the image display medium is presumed to be used, even if there are changes in the environment external to the image display medium. Consequently, there is no drop in the charge amount of the particle groups due to condensation of dew, so that favorable and stable display characteristics can be obtained.
According to a second aspect of the invention, an image display medium comprises: a pair of substrates, at least one of the substrates being light permeable; a gap disposed between the substrates; and plural kinds of particle groups differing in color and charging characteristic, the particle groups being sealed in the gap between the substrates and movable between the substrates by an electric field applied to the particles, wherein the water vapor content in the gap is 0.8 g/m3 or less.
According to the invention of the second aspect, the image display medium is provided with a transparent display substrate, the display substrate including an electrode and being disposed at the image display surface side of the image display medium, and a back substrate, the back substrate including an electrode and being disposed opposite to the display substrate. A gap is formed between the display substrate and the back substrate. Plural kinds of particle groups differing in color and charge characteristics are sealed in the gap. The particle groups can move between the pair of substrates by an electric field created by applying voltage between the pair of electrodes. The gap includes a water vapor content of 0.8 g/m3. Therefore, there is no dew condensation on the surfaces of the display substrate and the back substrate, or on the particle groups sealed in the gap in almost all environments in which the image display medium is presumed to be used, even if there are changes in the environment external to the image display medium. Consequently, there is no drop in the charge amount of the particle groups due to condensation of dew, so that favorable and stable display characteristics can be obtained.
According to a third aspect of the invention, an image display medium comprises: a pair of substrates, at least one of the substrates being light permeable; a gap disposed between the substrates; and plural kinds of particle groups differing in color and charging characteristic, the particle groups being sealed in the gap between the substrates and movable between the substrates by an electric field applied to the particles, wherein pressure in the gap is in a range in which dew does not condense in an environment in which the image display medium is used.
According to the invention of the third aspect, the image display medium is provided with a transparent display substrate, the display substrate including an electrode and being disposed at the image display surface side of the image display medium, and a back substrate, the back substrate including an electrode and being disposed opposite to the display substrate. A gap is formed between the display substrate and the back substrate. Plural kinds of particle groups differing in color and charge characteristics are sealed in the gap. The particle groups can move between the pair of substrates by an electric field created by applying voltage between the pair of electrodes. The gap includes a specific value of pressure, in a specified temperature range, for preventing dew condensation. Therefore, there is no dew condensation on the surfaces of the display substrate and the back substrate, or on the particle groups sealed in the gap in almost all environments in which the image display medium is presumed to be used, even if there are changes in the environment external to the image display medium. Consequently, there is no drop in the charge amount of the particle groups due to condensation of dew, so that favorable and stable display characteristics can be obtained.
According to a fourth aspect of the invention, an image display medium comprises: a pair of substrates, at least one of the substrates being light permeable; a gap disposed between the substrates; and plural kinds of particle groups differing in color and charging characteristic, the particle groups being sealed in the gap between the substrates and movable between the substrates by an electric field applied to the particles, wherein the pressure in the gap is 20 Torr or less.
According to the invention of the fourth aspect, the image display medium is provided with a transparent display substrate, the display substrate including an electrode and being disposed at the image display surface side of the image display medium, and a back substrate, the back substrate including an electrode and being disposed opposite to the display substrate. A gap is formed between the display substrate and the back substrate. Plural kinds of particle groups differing in color and charge characteristics are sealed in the gap. The particle groups can move between the pair of substrates by an electric field created by applying voltage between the pair of electrodes. The gap includes a pressure of 20 Torr or less. Therefore, there is no dew condensation on the surfaces of the display substrate and the back substrate, or on the particle groups sealed in the gap in almost all environments in which the image display medium is presumed to be used, even if there are changes in the environment external to the image display medium. Consequently, there is no drop in the charge amount of the particle groups due to condensation of dew, so that favorable and stable display characteristics can be obtained.